Passive threat warning systems detect potential missile threats to aircraft and other assets by sensing emitted energy in the ultraviolet, visible, and/or infrared bands emitted from the suspected threat. These systems rely on spectral sensors and algorithms to discern actual threats from background clutter, for example. At present, infrared sensor technology as applied to a missile threat warning application implements a system wherein the energy emitted in one narrow band, or color, in the range of approximately 4.4 μm to 4.8 μm is compared to the energy emitted in another narrow band in the range of approximately 3.9 μm to 4.1 μm. Discernment between, for example, a so-called “sun glint” and an earth-bound “hot object” or “hot event” such as a fire, a missile burn or a flamethrower is based upon the knowledge that the detectable energy associated with direct or reflected sunlight is markedly more intense in the 3.9 μm to 4.1 μm range than in the 4.4 μm to 4.8 μm range, while the emission spectrum of an earthbound “hot” or “warm” event is generally more intense in the 4.4 μm to 4.8 μm range than in the 3.9 μm to 4.1 μm range. Although such a “two-color sensor” facilitates the elimination from consideration as threats certain types of clutter sources (e.g., sun glints), current systems are generally incapable of further discerning whether an event not eliminated as clutter under the initial two-color regime presents an actual threat or whether, like direct or indirect sunlight, it is a benign energy emitter such as a warm factory smoke stack, a fire or a warm vehicle engine, for example. Accordingly, under current systems of threat discernment, numerous events not eliminated as sun-glint must be regarded as within the scope of potential threats to military assets and personnel, for example. This is problematic because personnel and non-human resources that could otherwise focus upon actual threats are instead assigned to at least the monitoring of benign events on the assumption that these events may present a threat. In still worse scenarios, ordnance may be expended in an attempt to neutralize an apparent threat. The unwarranted expenditure of ordinance amounts to waste and, furthermore, may (i) betray an otherwise secret position of personnel and assets and/or (ii) result in the unnecessary infliction of destruction and death.
Accordingly, there exists a need for a method and associated apparatus for discernment of threats that is more refined than that provided by, for example, a traditional “two-color” sensor and that can, more particularly, eliminate from consideration as apparent threats a larger scope of events with a greater degree of accuracy than previous discernment methods and devices.